1. Field of the Invention
The invention relates to storage-stable solutions of carbonated magnesium ethylate of the formula Mg(C.sub.2 H.sub.5 O).sub.2 (CO.sub.2).sub.n in ethanol.
The invention furthermore relates to a process for the preparation of storage-stable solutions of carbonated magnesium ethylate of the formula Mg(C.sub.2 H.sub.5 O).sub.2 (CO.sub.2).sub.n in ethanol either by reacting metallic magnesium with ethanol and CO.sub.2 or by reacting magnesium ethylate in ethanol with CO.sub.2.
The invention also relates to the use of storage-stable solutions of carbonated magnesium ethylate in ethanol for the preservation of paper and for the preparation of catalysts for the polymerization of olefins.
2. Background of the Invention
Magnesium alcoholates are, as a rule, not very soluble or virtually insoluble in the corresponding alcohols. An exception is magnesium methylate, which has a solubility of up to about 12% by weight in methanol.
A technically simple method for increasing the solubility of magnesium alcoholates is carbonation. Gaseous, liquid or solid CO.sub.2 is introduced into a suspension of the magnesium alcoholate in the corresponding alcohol. A soluble CO.sub.2 adduct forms. In the case of magnesium ethylate, the CO.sub.2 adduct is soluble with a concentration of more than 30% by weight in ethanol, whereas pure magnesium ethylate is virtually insoluble in ethanol.
Alcohol-soluble carbonated magnesium alkoxides are widely used. Thus, for example, magnesium alkoxides brought into solution by carbonation can be used in the long-term preservation of paper, in particular books, and can replace the zinc alkyls which are likewise used for this purpose but present problems during use.
A further field of use is the preparation of catalysts for the polymerization of olefins. For this purpose, spherical magnesium ethylate is prepared, for example, by spray drying or homogeneous precipitation of carbonated magnesium ethylate solutions and, if required, subsequent decarbonation.
It is known in principle that solutions of carbonated magnesium alcoholates can be prepared according to the two reaction schemes below: (1) reaction of metallic magnesium with an alcohol ROH and CO.sub.2 (equation 1) and (2) reaction of a magnesium alkoxide with CO.sub.2 (equation 2): EQU Mg+2 ROH+nCO.sub.2 .fwdarw.Mg(OR).sub.2 (CO.sub.2).sub.n +H.sub.2( 1) EQU Mg(OR).sub.2 +nCO.sub.2 .fwdarw.Mg(OR).sub.2 (CO.sub.2).sub.n( 2)
where R denotes an alkyl group and n is an integer such that O.ltoreq.n.ltoreq.2.
European Patent 0,236,082 teaches the preparation of carbonated magnesium alkoxides by reacting magnesium alkoxides with CO.sub.2 in a solvent. Preferred solvents are alcohols. In particular, the preparation of carbonated magnesium ethylate by reacting magnesium ethylate with CO.sub.2 in ethanol as a solvent is disclosed.
In "Reagents for Organic Synthesis" Vol. 1, page 631, Fieser and Fieser describe the preparation of carbonated magnesium methylate by two different routes: (1) reaction of a suspension of magnesium methylate in methanol with CO.sub.2 and (2) the reaction of magnesium turnings with methanol to give magnesium methylate. After the methanol has been partially stripped off at 50.degree. C. and reduced pressure, dimethylformamide is added as a solvent and CO.sub.2 is passed into this solution. The remaining methanol is distilled off, and a slightly yellow solution of carbonated magnesium methylate in dimethylformamide is obtained.
However, the alcoholic solutions of carbonated magnesium alkoxides according to the prior art are strongly yellow to red. Further, the discoloration can increase with increasing storage times. In addition, precipitation or gel formation can occur on storage for several weeks. The industrial use of such solutions is considerably limited. For example, colored solutions cannot be used for the long-term preservation of books. Further, solutions in which there is a danger of uncontrolled precipitation cannot be used for the preparation of catalysts based on magnesium alkoxide.